Amid worldwide discussion about global warming as a highly serious issue, the development of environmentally preferable refrigeration and air conditioning equipment have become increasingly important. Refrigerants have an impact on warming, and are greatly involved in the performance of refrigeration and air conditioning equipment; therefore, they play an important role in techniques to reduce emissions of carbon dioxide, which affects to warming.
In recent years, there have been various proposals for partially fluorinated propene (HFO) having a double bond in the molecule, which has lower global-warming potential (GWP) than conventionally known CFC (chlorofluorocarbon), HCFC (hydrochlorofluorocarbon), and HFC.
Known examples of HFO include HFO-1234yf (2,3,3,3-tetrafluoropropene), HFO-1234ze (E- or Z-1,3,3,3-tetrafluoropropene), and the like.
These substances are used singly or in the form of a composition (mixture) for various applications. As such compositions, for example, compositions comprising a mixture of HFC and HFO are known, as described in PTL 1 to PTL 4.
PTL 1 discloses a refrigerant composition comprising 36 to 50 mass % of 1,1,1,2-tetrafluoroethane (HFC-134a) and 50 to 64 mass % of 2,3,3,3-tetrafluoropropene (HFO-1234yf).
PTL 2 discloses a refrigerant composition comprising 30 to 50 mass % of difluoromethane (HFC-32) and 70 to 50 mass % of 2,3,3,3-tetrafluoropropene (HFO-1234yf).
PTL 3 discloses a refrigerant composition comprising difluoromethane (HFC-32), pentafluoroethane (HFC-125), and 2,3,3,3-tetrafluoropropene (HFO-1234yf), wherein the ratio of HFC-32/HFC-125/HFO-1234yf is in a range surrounded by points (0/21/79 mass %), (16.6/25.3/58.1 mass %), and (0/28.4/71.6 mass %) in a ternary diagram of the refrigerant composition, and the composition essentially comprises HFC-32.
PTL 4 discloses a heat transfer composition comprising (a) from about 20% to about 30% by weight of HFC-32, (b) from about 20% to about 30% by weight of HFC-125, (c) from about 0% to about 15% by weight of HFO-1234yf and from about 10% to about 30% by weight of HFO-1234ze, and (d) from about 15% to about 30% by weight of HFC-134a, with the weight percent being based on the total of the components (a) to (d) in the composition.
Although CFC and HCFC have lubrication performance, the lubrication performance of a composition comprising a mixture of HFC and HFO is lower than those of CFC and/or HCFC. In particular, when such a composition is used as a refrigerant composition, the lubrication performance as a whole is generally ensured by using a lubricating oil (refrigerant oil) in combination. In this respect, it is desirable to improve the lubrication performance of the composition comprising a mixture of HFC and HFO before a lubricating oil is used in combination. This improvement has become an issue.